Mercury switch



Nov. 17', 1936. c. E. GEHRAND ET AL MERCURY SWITCH Filed April 18, 1935 fie/zrmd ansom Patented Nov. 17, 1936 UNITED STATES MERCURY SWITCH Clarence E. Geln-and and Carl H. Larson, Elkhart, Ind., assignors to The Adlake Company, a corporation of Illinois Application April is, 1935, Serial No. 17,053

13 Claims. (01. 200-112) The principal object of this invention is to improve the operating characteristics of mercury switches of the type in which a magnetically responsive displacer shifts its position within a sealed envelope to cause a change in mercury level to determine the condition of an electrical circuit through two or more electrodes projecting into the envelope.

More specifically, this invention has for its primary objects to save power in the operation of mercury switches by obtaining maximum mercury displacement for minimum displacer travel; to provide means for using smaller air gaps than have heretofore been practical, with a resultant economy of power; to enclose the switch parts in a tube of relatively small diameter so that the operating coil will have less resistance per ampere turn; to avoid the use of cement in securing the component parts of the displacer together;

20 to eliminate guides from the displacer in alternating current-operated switches so that the magnetic material, of which the displacer is at least in part composed, may be placed closer to the walls of the switch envelope with a consequent 25 increase in the operating efficiency of the switch; to arrange the switch parts so that there is no danger of the displacer being fouled by other parts of the switch; to increase the carrying capacity of mercury switches without making a 30 corresponding increase in the size of the switch; to permit higher voltages to be used without danger ofhaving the switch break down; to provide a switch construction that lends itself to practical manufacturing methods and facilitates 35 assembly; and to obtain these numerous advantageous results without unduly increasing the cost of manufacture.

Further and other objects and advantages will become apparent as the disclosure proceeds and the description is read in conjunction with the accompanying drawing, in which Fig. l is a sectional view showing a power transfer switch made in accordance with this invention; 45 Fig. 2 is a view showing the position which the displacer takes when the associated coil is en ergized;

Fig. 3 is a horizontal sectional view taken on the line t-3 of Fig. l; 50 Fig. 4 is a horizontal sectional view taken on the line 4--4 of Fig. 1; Fig. 5 is an enlarged side elevational view of the displacer, illustrating particularly the manner in which the glass thimble and ironsleeve 55 are secured together by the buffer spring;'

Fig. 6 shows a displacer that is particularly useful for direct current operated switches;

Fig. '7 is a modified form of displacer for use in direct current relays;

Fig. 8 is a plan view of the guide washer that 5 is used with the displacers shown in Figs. 6 and 7; and

' Fig. 9 is a perspective view showing the manner in which the tops of the insulated electrodes may be bent to one side'in order to increase the cur- 10 rent carrying capacity of the switch.

For the purpose of this disclosure the invention has been shown applied to a power transfer switch, but it will be understood that many of the features of this invention may be used in other switches, and for that reason the appended claims should not be construed as limited to the particular association of parts that will hereinafter be specifically described, unless the prior art requires such an interpretation to preserve the validity of the claims.

The relay shown in Fig. 1 is intended to be used to transfer a load from one source of electrical energy to another, in response to a control circuit, but at no time should the load be connected simultaneously to both sources of electrical energy.

The relay includes a switch comprising a glass envelope Ill, through the bottom of which molybdenum electrodes ll, l2 and I3 are sealed, the latter two being surrounded by insulating sleeves I4 and IE to points slightly below the upper ends of the electrodes, leaving bared portions l6, ll, respectively.

The envelope contains a mercury fill l8, the level of which may be shifted by a magnetically responsive displacer or plunger, generally designated [9, comprising an elongated glass thimble 20, over which an iron sleeve 2 l is telescoped, the two parts being held in relative fixed position by a coil spring 22, of degasified pure iron wire which is tightly fitted on the upper portion of the thimble 20, and receives inwardly extending fingers 23 of the sleeve 2| between adjacent turns of the spring. The lower turns of the spring are close together, so that the fingers 23 of the sleeve 2! are firmly held in place, but the upper turns are spaced apart to act as a bufier in protecting the switch envelope from damage during shipment of the switch and over-energization of the operating coil.

The frictional engagement of the coil spring 22 with the thimble 20 and sleeve 2| obviates the necessity of using cement for securing these parts together, and since cement has a. tendency to 56 contaminate the mercury and shorten the life of the switch its elimination is very desirable.

Furthermore, the relative position of the thimble and sleeve can be very easily adjusted by rotating the sleeve with respect to the thimble, the coils of the spring acting as screw threads and causing the sleeve to move longitudinally of the thimble. This adjustability of the sleeve relative to the thimble is very convenient in obtaining the desired operating characteristics of the switch during manufacture.

The inwardly extending fingers 23 of the sleeve 2|, in addition to cooperating with the buffer spring 23 for the purpose of holding the sleeve and thimble in appropriate relative position, serve also to space the sleeve from the thimble and thus permit the mercury to drain to the bottom of the envelope after the switch has been inverted or tilted during shipment.

Before the switch envelope is sealed off, as indicated at 24, the envelope is evacuated, and a suitable gas fill introduced, as, for example, helium hydrogen, helium hydride, or the like.

The switch envelope III has an elongated protuberance 25 in its side wall adjacent to the base of the envelope,and the electrode I3, within its insulating sleeve I5, is positioned at least in part within this protuberance. The protuberance extends from the base of the envelope to a point slightly above the top of the electrode I3.

The magnetic circuit which operates the switch may be of the type shown in Figs. 1 and 3, in which the switch is mounted within the coil 26, or it may be of the type disclosed in Hedin Patent, No. 1,967,948, in which the switch is mounted exteriorly of the coil. The former mounting has the advantage of greater efficiency, but the latter is sometimes preferable in alternating current relays because it minimizes, due to a slight side pull, the vibration of the displacer within the envelope. This vibration, which is caused by the constantly changing magnetic field, is not apparent to the naked eye, but it results in a faint hum that is objectionable in some installations. Electro-mechanical relays operating on alternating current also hum, but to a greater extent.

In the form shown in Fig. 1 the coil 26 is tele scoped over the switch, and when the coil is energized the displacer I9 moves upwardly to the position shown in Fig. 2. The coil has an iron circuit associated with it that comprises a laminated iron yoke 21, the ends of which abut against pole sleeves 28 and 29, that are held in close contact with the yoke and in their proper relative position by fingers 30, secured to the ends of the yoke. The yoke is preferably made of Allegheny transformer steel, and the pole pieces may be of exceptionally pure Swedish iron, as, for example, Svea-metal, which is sold in the United States by the Swedish Iron and Steel Company, of New York.

The pole sleeves 26 and 29 fix the position of the air gap in the iron circuit with respect to the displacer, and are essential to efficient operation .of the relay. The distance between the pole sleeves 28 and 29 is maintained by a resilient non-magnetic sleeve 3|, preferably of brass or bakelite, having a longitudinal slit 32 in its side wall to permit it to be telescoped over the switch envelope and frictionaliy engage it. In addition to {maintaining the distance between the pole sleeves, the sleeve 3I also supports the switch within the coil.

When the coil 26 is de-energized, the displacer I9 seats upon a molybdenum coil spring 33 (Fig. 1) that rests on the floor of the switch envelope and is anchored in place by having adjacent turns engaging the central electrode l2 (see Fig. 4). In this position the thimble 20 cups the central electrode I2 and forms a gas trap over the electrode which holds the mercury away from the bared end I6 of the electrode, but the displacement of mercury is sufllcient to bridge the electrodes II and I3.

When the coil 26 is energized the displacer I! moves upwardly to the position shown in Fig. 2, lowering the mercury level to a point below the top of the insulating sleeve I5 and hence breaking the circuit between the electrodes II and I3, but at the same time permitting the mercury to contact with the bared end I6 of the central electrode I2, thus closing the circuit between the electrodes II and I2. The electrodes l2 and II are of such length with respect to the mercury fill and the displacer that as the displacer is lifted from the position shown in Fig. 1 to that shown in Fig. 2 the mercury level will fall below the top of the insulating sleeve I5, prior to the time that mercury is permitted to rise above the top of the insulating sleeve I4, so that the circuit between the electrodes II and I3 is completely broken before the circuit through electrodes II and I2 is completed.

Conversely, when the displacer falls from the position shown in Fig. 2 to that shown in Fig. l, by the de-energization of the coil 26, the mercury surrounding the bared end of the electrode I2 will be forced below the top of the insulating sleeve I4 before sufficient mercury is displaced to contact with the bared end I1 of the electrode I3. Hence there is no overlap between the two circuits on either upward or downward movement of the displacer.

When the relay operates on alternating current, the iron sleeve 2| is preferably made of cold rolled steel, case hardened and ground. When the coil 26 is operated on direct current, a displacer of the type shown in Figs. 6 and '7 is used. The iron sleeve 34, in this case, is made of high quality soft iron, as, for example, Svea metal. It is necessary to use a soft iron in the direct current relay because a hard iron would retain its magnetism and cause the relay to stick in energized position.

Because of the softness of the iron used in the sleeve 34, it is desirable to provide case hardened guide washers 35, preferably of tool steel, the washers having a plurality of smoothly rounded guide lugs 36 for positioning the displacer within the switch envelope.

It is convenient to hold the sleeve 34 and washers 35 in fixed relation with respect to the thimble 36 by springs 31 and 38, which are tightly telescoped over the thimble 36.

Inasmuch as the spring 31 merely serves as a seat for the lower guide washer and the parts above, the thimble may be slightly enlarged, as

indicated at 39 in Fig. 7, and thus obviate the necessity of using the spring 31. The bulb 39 also serves the purpose of imparting a quick movement to the mercury when the circuit ill be made of relatively large diameter and thickness, whereby a substantial mercury displacement can be effected with very short plunger travel. It is obvious that if the switch envelope had a uniform diameter corresponding to the distance between the protuberance 25 and the opposite side wall, it would take a longer plunger stroke to obtain the same change in mercury level. By maintaining the displacer stroke as short as possible, the air gap between the top of the displacer and the top pole sleeve 28 may be reduced to a minimum, thus saving in the power required to move the displacer to its uppermost position.

By placing one of the electrodes within the protuberance 25, instead of making the tube of uniform diameter corresponding to the distance between the protuberance 25 and the opposite sidewall of the envelope, the coil 26 will have less resistance per ampere turn than it would otherwise have and here again power'is saved.

The placement of the electrode 3 within the protuberance 25 permits the electrodes to be spaced farther apart, which not only results in better clearance for, the switch parts but also enables the use of electrodes of the type shown in Fig. 9, in which the bared ends of the electrodes are bent over to protect the top of the-insulating sleeves, as disclosed in Larson Patent No. 1,967,247, the extra bend 40 providing a better contacting surface ll and increasing the current carrying capacity of the switch. It will be understood that the bared ends of electrodes l2 and I3 may be formed in the manner shown in Fig. 9, where it is desirable to have additional current carrying capacity.

The increased spacing between the electrodes l2 and I3, aiforded by placing the electrode l3 within the protuberance 25, means that thicker insulating sleeves may be used around the electrodes with a consequent increase in the voltage capacity of the switch.

The iron sleeve 2| being made of hardiron for use with alternating current, and being at all times above the mercury level so that mercury does not enter the annular space between the sleeve and the switch envelope during the operation of the switch, can be used without providing guides such as shown in Larson Patent No. 1,967,950, for example. (The guides were heretofore necessary to permit the mercury to enter this annular space, but the mercury caused much friction.) This means that the sleeve 2| is closer to the envelope than was heretofore possible, and this lessening of the air gap results in a corresponding increase in the eificiency of the switch.

Many of the ieaturFs of this invention may be used in conjunction with time delay switches of the type disclosed in Larson application Serial No. 748,586 in which gas is allowed to slowly escape through an opening in the top of the displacer.

It will be understood that the invention is applicable to pull down relays as well as pull up relays, the former being of the type in which magnetic force is used to lower the displacer and buoyancy to lift it, and the latter depending upon gravity to lower the displacer and magnetic force to lift it.

We claim as our invention:-

1. In a switch of the class described, a switch envelope, spaced electrodes in the envelope, a

ercury fill, a magnetically responsive displacer for shifting the mercury level comprising an iron sleeve telescoped over an elongated thimble of non-magnetic material, means for holding the sleeve and thimble in fixed relation, said means comprising a coil spring frictionally engaging the thimble, and a finger on the sleeve extending between adjacent turns of the spring.

2. In a switch of the class described, a switch envelope, spaced electrodes in the envelope, a mercury fill, a magnetically responsive displacer for shifting the mercury level comprising an elongated tubular body over which an iron sleeve' of non-magnetic material is telescoped, and means for holding the sleeve and body in fixed relation, said means including a coil spring frictionally engaging the body and a finger on the sleeve extending between adjacent turns of the spring.

3. In a switch of the class described, a switch envelope, spaced electrodes in the envelope, a mercury fill, a magnetically responsive displacer for shifting the mercury level comprising a tubular body, an iron sleeve telescoped over the body and spaced therefrom by inwardly extending fingers at the top and bottom of the sleeve, and means for securing the sleeve to the body including a coil'spring frictionally engaging the body, said sleeve having an outer cylindrical surface free of projections and being out of contact with the mercury at all portions of the displacer.

4. In a switch of the class described, a switch envelope, spaced electrodes in the envelope, a mercury fill, a magnetically responsive displacer for shifting the mercury level, comprising an iron sleeve telescoped over an elongated thimble, a coil spring tightly fitted over the thimble, and a finger on the sleeve extending between adjacent turns of the spring, whereby the sleeve is held in fixed relationto the thimble but may be moved longitudinally thereof by rotation of the sleeve relative to the thimble.

5. In a switch of the class described, a switch envelope having an elongated longitudinally extending protuberance in its side wall adjacent to the base of the envelope, spaced electrodes sealed through the base of the envelope including one substantially centrally positioned and one positioned at least in part within the protuberance, a magnetically responsive displacer for shifting the mercury level, said displacer including a thimble adapted to cup the central electrade to force mercury away from said electrode when the displacer is moved to its lowermost position, the ratio of the efiective cross sectional area of the displacer to the cross-sectional area of the mercury fill being relatively high whereby the length of displacer travel necessary for op erating the switch is held to a minimum.

6. In a switch of the class described, a switch envelope having an enlarged protuberance in its side wall adjacent to the base of the envelope, spaced electrodes sealed through the base of the envelope, one of which lies at least in part within the protuberance, and a magnetically responsive displacer for shifting the mercury level, said displacer including a thimble presenting arelatively large opening at its lower end to the mercury and adapted to trap gas when the displacer is moved downwardly, the ratio of the effective cross-sectional area of the displacer to the crosssectional area of the mercury fill being relatively high whereby the length of displacer travel necessary for operating the switch is held to a minimum. 7

7. In a mercury switch of the class described, a switch envelope, a mercury fill, a plurality of spaced electrodes sealed through the base of the envelope, a magnetically responsive displacer for shifting the mercury level to open or close the circuit through the electrodes, and means for minimizing the length of displacer travel necessary for operating the switch, said means comprising a protuberance in the lower side Wall of the envelope and an electrode in the protuberance whereby the ratio of the eifective cross-sectional area of the displacer to the cross-sectional area of the mercury fill may be made relatively high.

8. In a mercury switch of the class described, a switch envelope having a protuberance in its side wall adjacent to the base of the envelope, a mercury fill, a plurality of spaced electrodes sealed through the base of the envelope, a magnetically responsive displacer for shifting the mercury level to open or close the circuit through the electrodes, one of said electrodes being positioned substantially within the protuberance whereby maximum displacement is obtained for minimum plunger travel, said displacer compris ing an iron sleeve telescoped over a tubular body of non-magnetic material, the iron sleeve having a plurality of inwardly extending fingers spacing the sleeve from the body.

9. In a mercury switch of the class described, a switch envelope, spaced electrodes pinchsealed into the base of the envelope, a mercury fill, a displacer for shifting the mercury level to determine the condition of the electrical circuit through the electrodes, said switch envelope being of cylindrical form except for a substantially uniform elongated protuberance in the side wall of the envelope, said protuberance extending lengthwise of the envelope and terminating at the pinchseal base thereof, one of the electrodes being positioned vertically within the protuberance.

10, For use in a mercury switch of the class described, a switch envelope, a plurality of electrodes sealed into the envelope base, an insulating sleeve surrounding one of the electrodes to a point slightly below the top of the electrode, and a longitudinal protuberance in the side wall of the switch envelope adapted to receive said one electrode.

11. In a mercury switch of the class described characterized by high operating efllciency and comprising a switch envelope of substantially uniform tubular form except for a relatively slight vertical protuberance in its side wall adjacent to the base of the envelope, a plurality of electrodes projecting into the envelope one of which lies substantially within the protuberance, a mercury fill, a magnetically responsive displacer for shifting the mecury level, said diaplacer including an iron sleeve having an outer cylindrical surface free of projections and pool-- tioned so that it is at all times out of the mercury, said sleeve having its outside diameter but slightly less than the inside diameter of the envelope, whereby the air gap between the external magnetic circuit and the displacer is held to a minimum.

12. In a switch 01' the class described, a switch envelope, spaced electrodes in the envelope, a mercury fill, a magnetically-responsive displacer for shifting the mercury level thereby to change the condition of the electrical circuit through the electrodes, and means for minimizing the length of displacer travel necessary for operating the switch, said means including a longitudinally extending protuberance in the lower side wall of the envelope and an electrode in the protuberance whereby the ratio the effective ores-sectional area of the displacer to the cross-sectional area of the mercury fill may be kept relatively high.

13. For use in a mercury switch of the class described, a hollow displacer comprising an inner sleeve of non-magnetic material and an outer sleeve of magnetic material, and a bulge in the non-magnetic sleeve below the magnetic sleeve.

CLARENCE E. GEHRAND. CARL H. LARSON. 

